EDGE denotes "Explain, Demonstrate, Guide, Enable" and comes from a concept for youth leadership development training. Biotechnical and enzymatic micro-flow reactors are a young discipline. Here the enthusiasm level mirrors its technological growth and vice versa. Rather than being a linear function, enthusiasm first goes down after sudden realization of all bottlenecks and technological shortcomings which are to overcome in a Hercules task action. However, with increasing provision of technology and security in its performance, the enthusiasm level rises again. This "valley of death" needs to be crossed to bridge to a market. The enzymatic micro-flow reactors mirror the above depicted development of their counterparts -the chemical microreactors -which is already about 20 years old. This "Déjà vu" forms a feature story which encompasses a review about enzymatic microreactors and their synthetic applications which are shown in all their facets. This compilation is structured in chapters about reactor and enzyme support technology, transport intensification, chemical intensification, process-design intensification, and finally first steps into the bio-based economy.
Threonine aldolase (TA) from Thermotoga maritima was immobilized on an Eupergit support by both a direct and an indirect method. The incubation time for the direct immobilization method was optimized for the highest amount of enzyme on the support. By introducing the immobilized TA in a packed-bed microreactor, a flow synthesis of phenylserine was developed, and the effects of temperature and residence time were studied in particular. Calculations of the Damköhler number revealed that no mass transfer limitations are given in the micro-interstices of the packed bed. The yield does not exceed 40% and can be rationalized by the natural equilibrium as well as product inhibition which was experimentally proven. The flow synthesis with the immobilized enzyme was compared with the corresponding transformation conducted with the free enzyme. The product yield was further improved by operating under slug flow conditions which is related to the very short residence time distribution. In all cases 20% diastereomeric excess (de) and 99% enantiomeric excess (ee) were observed. A continuous run of the reactant solution was carried out for 10 hours in order to check enzyme stability at higher temperature. Stable operation was achieved at 20 minute residence time. Finally, the productivity of the reactor was calculated, extrapolated to parallel run units, and compared with data collected previously.2168
The continuous flow nitration of acetophenone followed by reduction of the meta isomer has been demonstrated using simple tubular reactors. Because of ease of separation of the desired isomer from the first step, both steps are made continuous, but separately. The continuous flow nitration was carried out in a safe manner in a shorter reaction time than the conventional approach. The choice of micromixer was seen to affect the performance of the nitration reaction. The effect of different parameters on the yield of the desired product was studied. The reduction step with sodium sulfide was found to be economical and could be carried out efficiently at 70°C using sodium sulfide in ethanol, using a silicone tube. Both steps were demonstrated for several hours, yielding a sufficiently large quantity (∼100 g) of m-aminoacetophenone at lab scale in a single day using simple tubular reactors.
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